This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
AP: Wi-Fi Access Point
BSS: Basic Service Set
CdW: Contention Window
CCA: Clear Channel Assessment
CST: Clear-to-Simultaneous-Transmission
DCF: Distributed Coordination Function
DIFS: DCF Interframe Space
FCS: Frame Check Sequence (Cyclic Redundancy Check (CRC))
LTE: Long Term Evolution
MAC: Medium Access Control
MCS: Modulation Coding Scheme
NAV: Network Allocation Vector
OBSS: Overlapping-BSS
RA: Receiver Address
RST: Request-Simultaneous-Transmission
SIFS: Short Interframe Space
STA: Wi-Fi Station (non AP)
STW: Simultaneous Transmission Window
TA: Transmitter Address
The IEEE 802.11 standard for Wireless Local Area Networks (WLANs), commonly known as Wi-Fi, has been broadly adopted to provide users with wireless broadband access to the Internet. With the increase on the demand for wireless Internet access, dense Wi-Fi deployments have become more common in both residential and office environments. For a dense Wi-Fi deployment there can be a high density of Wi-Fi terminals and networks operating without coordination and with overlapping coverage.
In a typical mode of Wi-Fi operation an Access Point (AP) bridges a Basic Subscriber Set (BSS) of wireless stations (STAs) to a wired Ethernet network. Wi-Fi uses a contention-based channel access protocol known as Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA). In CSMA/CA operation Wi-Fi nodes need to ‘listen’ to a channel prior to transmitting. This procedure is known as Clear Channel Assessment (CCA). Nodes in CCA may receive transmissions from one or more other nodes. These received transmissions are understood to indicate that the channel is occupied. In response to the channel being occupied the node defers its own transmission for some random duration of time (known as backoff).
One approach employs DCF that uses a CSMA/CA with a binary exponential backoff algorithm. DCF requires a station wishing to transmit to listen for the channel status for a DIFS interval. If the channel is found busy during the DIFS interval, the station defers its transmission. In a network where a number of stations contend for the wireless medium, if multiple stations sense the channel busy and defer their access, they will also virtually simultaneously find that the channel is released and then try to seize the channel. As a result, collisions may occur. In order to avoid such collisions, DCF also specifies random backoff, which forces a station to defer its access to the channel for an extra period.
As can be appreciated the backoff situation occurs more frequently in a dense deployment with overlapping BSSs (OBSSs), which causes a degradation of Wi-Fi performance in terms of throughput, latency and user quality of service (QoS).